1. Technical Field
This disclosure relates generally to thin-film magnetoresistive (MR) read sensors (i.e. read heads) and particularly to the enhancement of micro-magnetic read width of such sensors by the use of different shield materials and configurations.
2. Description
The demand for data storage capacity in today's information technology has driven the increase of recording density in magnetic storage. One of the components in magnetic storage that determines the recording density is the read head sensor, which is based on a spin valve magnetoresistance (SVMR) configuration. As the recording density increases to the level of Gb/in2, the size of the recording bit in the magnetic storage medium shrinks into the nanometer range. The size of the read head sensor, therefore, needs to be of that same dimensional order in order to read the bit signal accurately. Typically the cross-sectional area of the read sensor is smaller than 0.1×0.1 microns at the air bearing surface (ABS) of the read/write head for recorded media areal density of 100 Gb/in2 and above.
Current technology utilizes the tunneling magnetoresistive (TMR) effect in the SVMR sensor. Typically, the sensor has a bottom spin valve configuration. This sensor structure includes two ferromagnetic layers, a top and a bottom, separated by an ultra-thin dielectric tunneling layer. The top ferromagnetic layer is a free layer (FL) whose magnetic moment is free to respond to the changing fields produced by the recorded media, whereas the bottom ferromagnetic layer is a reference layer (denoted AP1, for “first antiparallel layer”) whose magnetic moment is fixed in space. The dielectric tunneling layer is usually made of MgO or AlOx.
The layer AP1 is pinned by yet another ferromagnetic layer (AP2, for “second antiparallel layer”) through a synthetic anti-ferromagnetic (SAF) effect which creates antiparallel magnetic moments in AP1 and AP2. The magnetic moment of the AP2 layer is pinned in spatial direction by an anti-ferromagnetic layer at its bottom surface. When an external magnetic field is applied to the sensor by passing it over a recording medium at its ABS, the FL magnetization will rotate corresponding to the direction of the magnetic field it experiences. Depending upon the memory state (“0” or “1”) of the magnetic medium closest to the FL, which translates into the direction of its magnetic field, the magnetization (magnetic moment) of the FL will rotate to a direction either parallel or anti-parallel to that of the AP1. When an electric current passes through the sensor in order to read the FL state of magnetization, the resistance R will change in accord with the joint magnetization states of FL and An R is low when the magnetization of the FL is parallel to the AP1 and high when antiparallel. Thus the read head sensor will register a bit as a “0” or “1”.
The typical design of a read head sensor is based on an abutting junction configuration in which the sensor is surrounded by shields (bottom shield S1, top shield S2 and side shields) to isolate it from unwanted external fields. The sensor is also etched at the back edge to produce an island shape with dimensions in nm×nm range. At this size range, the FL of the sensor will encounter significant demagnetization interference from outside. Therefore, a longitudinal biasing field from side shields is necessary to anchor the magnetization of the FL and keep it from fluctuation. Conventionally, the side shields consist of a hard bias layer (a layer of “hard” magnetic material) formed adjacent to each side of the free layer of the sensor at the ABS. As the critical dimensions of the sensor element become smaller, the FL becomes more volatile and more difficult to bias. This biasing scheme using a hard bias layer has become problematic due to randomly distributed hard magnetic grains within the hard bias layer. To mitigate the problem, we have proposed in related applications Ser. Nos. 13/785,227 and 13/865,269 (which are fully incorporated herein by reference) a different scheme to use soft magnetic layers (permalloy, supermalloy, MU metal, etc) to form the side shields.
Referring to FIG. 1, there is shown a schematic graphical illustration of a read-back cross track profile (denoted the “micro read width” or μMRW) which is obtained by scanning the read head across the width of a given data track and plotting the read-back amplitude vs. the off-track distance (distance from track center). The 100% amplitude is the relative strength of the read-back signal when the head is positioned perfectly at the track center. μMRW-10% (the x-axis distance −x1 and x1) and μMRW-50% (the x-axis distance −x2 and x2) are the 10% and 50% micro magnetic read widths that are defined by the width of the cross track profile in FIG. 1 at relative amplitudes corresponding to 10% and 50% of the track center amplitude, respectively. A higher cross track resolution requires a small μMRW and better μMRW sharpness which means the ratio of μMRW-10% and μMRW-50% should be as close to 1 as possible.
In this disclosure, we propose a shield scheme to improve the μMRW sharpness by using high magnetic moment wrap shields on the side and top shields.
The prior arts disclose various attempts at resolving sensor performance problems by the use of various shield structures and materials. Examples are: Lin, (U.S. Pat. No. 7,599,153); Lin, (U.S. Pat. No. 7,606,009) and Nishida et al. (U.S. Pat. No. 7,450,349). However, none of these attempts have addressed the problem in the same manner and with the same effect as the method to be summarized below and then described in further detail herein.